In a typical mold molding method, a mold is molded by filling a frame, in which a model is placed, with self-hardening sand obtained by kneading sand, a binder, and hardening accelerator, and removing the model (hereinafter referred to as “model removal”) after the self-hardening sand is hardened, so that a shape of the model is transferred to the hardened self-hardening sand.
There has been known a mold molding method in which a mold having a complicated shape necessary for casting a product having a twisted shape such as a male rotor or female rotor of a screw compressor is molded using a model by the above mold molding method (see, for example, Patent Literature 1).
By using the technique disclosed in Patent Literature 1, it is possible to reduce a process margin of a cast product and achieve a near-net-shape cast product.